This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The Nuclear Pore Complex (NPC, about 50 MDa) is the sole passageway for the transport of macromolecules across the nuclear envelope. The pore plays a key role in numerous critical cellular processes such as transcription, and many of its components are implicated in human diseases such as cancer. Previous work provided the first description of the macromolecular architecture of the yeast NPC. This structure defined the relative positions and proximities of its 456 constituent nucleoporin (nup) proteins, based on spatial restraints derived from experimental data. Further elucidation of the evolutionary origin and transport mechanism of the NPC will require higher resolution information. To help improve upon the resolution and accuracy of the NPC structure, we propose to obtain small angle x-ray scattering (SAXS) data at SSRL. We are preparing a set of single protein, protein domain, and small NPC subcomplex samples for SAXS analysis. We will apply our Integrated Modeling Platform (IMP) software to incorporate a diverse set of experimental data, including SAXS spectra, as spatial restraints, to determine the three dimensional structures of these subcomplexes and proteins. We are specifically focusing on components of two subcomplexes, the 7-protein Nup84 subcomplex, and the 4-protein Nup170 complex, for which complementary experimental data are available. We have already used a similar protocol, to map different functional states of human Hsp90.